1. Field of the Invention
The present invention relates to a measuring method and apparatus and, more particularly, to a measuring method and apparatus capable of optimally correcting a geometrical measurement error inherent in a machine control gage, a surface roughness profile measuring device or the like incorporated in a grinding machine or the like.
2. Description of the Related Art
In machine control gages (automatic sizing devices), surface roughness contour measuring devices or the like incorporated in grinding machines or the like, a measuring head is used which has a seesaw member having a probe at its end and supported by a supported member so as to be rotatable on the supporting member, an urging member which urges the seesaw member in one direction, and a detector which is provided on the opposite side of the seesaw member from the probe as seen from the supporting member, and which detects a displacement of the probe by detecting a displacement of the seesaw member.
This detector is, for example, an optical digital scale including a reading head fixed on the measuring head body and a circular-arc scale attached to the seesaw member, or a linear voltage differential transducer or transformer (LVDT) (popularly called a differential transformer) including a differential coil portion fixed on the measuring head body and a core attached to the seesaw member and inserted in the differential coil portion.
The amount of movement of the probe is detected as a pulse count value of the optical digital scale (detected as a change in voltage in the case of LVDT). This detected value is processed in a computation processing unit to be obtained the amount of movement.
In machine control gages, a measuring head constituted by one seesaw member and capable of measuring a displacement in one place by one probe, a caliper-type measuring head having a pair of seesaw members and capable of pitching an object to be measured between two probes opposed to each other to measure the outside diameter of the object, and the like are used.
In the case of measurement of the position of a flat surface (thickness, for example) with such a seesaw-type measuring head, an error occurs since a displacement is measured as an angle. In the case of measurement of a curved surface, e.g., measurement of the outside diameter of a cylindrical work, an error occurs due to a shift of the probe contact point.
To reduce the influence of these geometrical error factors, various devices or methods have been proposed (see, for example, Japanese Patent Application Publication No. 10-19545).
In the size measuring apparatus described in Japanese Patent Application Publication No. 10-19545, correction data for correction through the entire measurement range is obtained in advance and is stored in a memory. At the time of measurement, a measured value is corrected by reading out the corresponding correction data from the memory.